Tuberculosis and HIV/AIDS represent the major infectious causes of death in the world, and tuberculosis (TB) is the attributable cause of death in a third of AIDS patients in Africa. Drug resistance to TB is emerging in Europe and Asia, drug treatment regimens are long and expensive and compliance is limited. For these reasons, we propose to bring a multidisciplinary approach, joining molecular genetics and immunology, to developing safe and effective live attenuated vaccines against TB. Since peak age of disease is 15-25y, we believe a live attenuated vaccine that induces long enduring immunological memory will provide the most useful protection against disease. In previous work we have developed tools to genetically manipulate slow growing mycobacteria, including the capability of creating specific deletion mutants to attenuate virulent M tuberculosis. One aim is to test the hypothesis that M tuberculosis represents a better vaccine candidate than BCG, to create and test auxotrophic mutants, growth mutants and persistence mutants of M. tuberculosis for safety and immunogenicity in mice. A second is to determine the optimal duration of growth of vaccine strains in vivo for the development of immunological memory responses, particularly through the use of regulated promoters. This will also allow us to elucidate similar requirements for producing tissue damage. Our final aim remains to understand the immunological mechanisms of protection against experimental tuberculosis, particularly exploring the role of innate responses mediated by the Toll-like receptor family, the minimum epitope and antigen requirements for protection, and the possible role of cytotoxic T-lymphocytes (CTL) in protection.